This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-178160, filed Jun. 14, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a power supply device and an information processing apparatus and, more particularly, to a power supply device for generating a predetermined power supply voltage and an information processing apparatus having this power supply device.
The recent spread of information processing apparatus is remarkable in every field. In particular, portable information processing apparatus such as portable computers and personal digital assistants are used in a wide variety of fields as their capabilities have improved.
Batteries are often used as power supplies of such information processing apparatus. Since these information processing apparatus are presently used more frequently than before, it is desired by the users to reduce the consumption power and prolong the driving time of the information processing apparatus.
To this end, it is being attempted to reduce the operating power supply voltage of an MPU (Micro Processor Unit) as one constituent semiconductor device of an information processing apparatus.
On the other hand, as the semiconductor device fabrication technologies have improved in recent years, micropatterning of the structures of semiconductor devices such as an MPU is in progress. In micropatterned semiconductor devices, the voltage of an operating power supply is lowered to prevent dielectric breakdown. That is, the operating power supply voltages of semiconductor devices such as an MPU in information processing apparatus are increasingly lowering.
Also, for the sake of energy saving, technologies which dynamically change the operating frequency and operating voltage of an MPU have been developed. In an information processing apparatus using this type of an MPU, control of a power supply voltage to be supplied to the MPU must also be taken into consideration.
The arrangement of a conventional power supply device will be described below with reference to an accompanying drawing.
FIG. 1 is a circuit diagram showing the arrangement of this conventional power supply device. A power input terminal 601 inputs power to be converted into output power. A power output terminal 602 outputs power converted by a DC/DC converter IC 603 to be described later. The DC/DC converter IC 603 is an IC which controls the conversion of the input power from the power input terminal 601 into power to be output to the power output terminal 602.
An MPU 600 executes processing of an information processing apparatus incorporating this power supply device. This MPU 600 also sets the value of an output power supply voltage from this power supply device into the DC/DC converter IC 603.
The MPU 600 sets this value by setting a 5-bit D/A code (digital/analog code) in the DC/DC converter IC 603. The set value is reflected on the value of a reference voltage in the DC/DC converter IC 603. A voltage range thus settable by the MPU 600 is called an adjustment range.
A converter circuit is formed by the DC/DC converter IC 603, a capacitor 604, a coil 605, a FET 606, and a rectifier 607. The capacitor 604 and the coil 605 function as an output filter. The FET 606 serves as a switch. The output power supply voltage from the power output terminal 602 can be adjusted by controlling switching of this FET 606 by the DC/DC converter IC 603.
A feedback terminal 608 of the DC/DC converter IC 603 feeds the converted voltage from the converter circuit back to the DC/DC converter IC 603.
Upon receiving this feedback, the DC/DC converter IC 603 checks whether voltage conversion is appropriately performed. This check is done by comparing the feedback value with the above-mentioned value of the reference voltage corresponding to the setting by the MPU 600.
If there is a large difference between the feedback voltage value and the value of the reference voltage, the DC/DC converter IC 603 controls switching of the FET 606, thereby appropriately performing voltage conversion.
With this arrangement, the DC/DC converter IC 603 monitors the voltage fed back to its feedback terminal and controls the operation of the switch, thereby varying the output voltage within the adjustment range settable by the MPU 600.
For a voltage exceeding the adjustment range, however, the DC/DC converter IC 603 cannot perform any setting exceeding this range, so this power supply device cannot control the voltage. In particular, a DC/DC converter having a narrow adjustment range is highly likely to be unable to control a voltage required by an MPU, if the driving voltage of the MPU dynamically changes.
Even when the adjustment range is wide, accuracy often lowers near the upper and lower limits of the range. If the accuracy of voltage control lowers, it becomes difficult to drive a semiconductor device, such as an MPU, having strict conditions on the accuracy of operating voltage.
The above conventional technology cannot vary the output voltage outside the adjustment range set by a D/A converter or the like. If this adjustment range is narrow and the power supply voltage required by an MPU dynamically changes to the outside of the adjustment range, this voltage exceeds the possible output range of a DC/DC converter. This makes the conventional DC/DC converter unable to supply power to the objective MPU.
The present invention has been made to solve the above problem, and has as its object to provide a power supply device capable of stably supplying power even to an MPU whose necessary power supply voltage dynamically changes, and an information processing apparatus having this power supply device.
To achieve the above object, according to the first aspect of the present invention, there is provided a power supply device comprising
a power input terminal which inputs a DC voltage; a DC/DC converter, having a feedback terminal, which converts the input DC voltage from the power input terminal;
a power output terminal which outputs the DC voltage converted by the DC/DC converter;
a voltage generator which supplies a voltage; and
a resistor connected between the power output terminal and the voltage generator, wherein the feedback terminal is connected between the register and voltage generator.
In the power supply device having this arrangement, the input voltage to the feedback terminal is made to have a value different from the output voltage from the power output terminal, by the resistor connecting the power output terminal and the voltage generator. Accordingly, a lower voltage can be supplied.
According to the second aspect of the present invention, there is provided a power supply device comprising
a power input terminal which inputs a DC voltage;
a DC/DC converter, having a feedback terminal, which converts the input DC voltage from the power input terminal;
a power output terminal which outputs the DC voltage converted by the DC/DC converter;
a current source which supplies a predetermined current; and
a resistor connected between the power output terminal and the voltage generator, wherein the feedback terminal is connected between the register and current source.
In the power supply device having this arrangement, the input voltage to the feedback terminal is made to have a value different from the output voltage from the power output terminal, by the resistor connecting the power output terminal and the current source. Accordingly, a lower voltage can be supplied.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.